Digital printing machines can take on a variety of configurations. One common process is that of electrostatographic printing, which is carried out by exposing a light image of an original document to a uniformly charged photoreceptive member to discharge selected areas. A charged developing material is deposited to develop a visible image. The developing material is transferred to a medium sheet (paper) and heat fixed.
Another common process is that of direct to paper ink jet printing systems. In ink jet printing, tiny droplets of ink are sprayed onto the paper in a controlled manner to form the image. Other processes are well known to those skilled in the art. The primary output product for a typical digital printing system is a printed copy substrate such as a sheet of paper bearing printed information in a specified format.
The output sheet can be printed on one side only, known as simplex, or on both sides of the sheet, known as duplex printing. In order to duplex print, the sheet is fed through a marking engine to print on the first side, then the sheet is inverted and fed through the marking engine a second time to print on the reverse side. The apparatus that turns the sheet over is called an inverter.
In printer systems it is desirable to have the option of multiple finishing units. Some have bypass systems but many do not which precludes additional finishing options. Finishing systems can include simple stackers through fully integrated finishing systems with staplers, stitchers or other finishing options. A customer with one printer may wish to sort output to more than one of these finishers even as part of the same job or back to back jobs. This requires that the system be able to sort the outgoing media to the desired finishing equipment. This is not possible with current systems where integrated bypass routes are not available. A diverter and bypass will redirect sheets to a different path, but the new path typically lies directly above or below the process path. In the event that bypass systems are available, the only option is inline which lengthens the system to an unacceptable extent.
Attempting to redirect the media with a rotating or intermittent motion apparatus is limited by inertias of the system. Such a system is not capable of meeting throughput speeds when PPM rates increase or smaller inter copy gaps are required. Such a system cannot redirect media at full process speeds.
Current RAT (Right Angle Transfer) systems change the sheet orientation from SEF Portrait to LEF Landscape or Landscape to Portrait for any system that is at a right angle to the printer process path. LEF is Long Edge Feed, or Landscape. SEF is Short Edge Feed, or Portrait.
FIG. 1 (prior art) shows a state-of-the-art digital printing machine 84. Printer 84 includes a marking engine 86. Printer 84 has an inverter 92 to turn the sheet over for duplex printing. Typically, as the sheet is inverted, the trail edge becomes the lead edge. This construction also tends to limit the speed at which sheets can be conveyed through inverter 92, because the sheet is stopped and reversed and accelerated.
Accordingly, there is a need to provide a media sheet routing system that will allow multiple finishing systems to be attached to a high speed printer.
There is a further need to provide a media sheet routing system of the type described and that will selectively direct media sheets to each of the multiple finishers without a skipped pitch or change in intercopy gap.
There is a yet further need to provide a media sheet routing system of the type described and that will match the high production rate of a digital printing machine.
There is a still further need to provide a media sheet routing system of the type described and that will not change the sheet orientation from SEF to LEF or from LEF to SEF.
There is an additional need to provide a media sheet routing system of the type described and that is mechanically simple and robust, thereby minimizing cost and avoiding the problems associated with the prior art.